The present invention relates to non-destructive diagnostic equipment, and particularly to eddy current diagnostic equipment which is suited for measuring thickness, for detecting flaws and for measuring the size of flaws in structures such as conduits.
An eddy current method has been extensively used to non-destructively inspect metallic materials, and the state of the art is now such that flaws can be precisely measured. The conventional method of precisely measuring flaws based upon the phase method has been announced in the journal Mitsubishi Jyuko Giho entitled "Eddy Current Flaw Detecting Technique for Heat Conducting Pipes", Vol. 13, No. 3, May 1976, pp. 33-39.
With this method, the phase of flaw detection signal changes depending upon the depth of the flaw and the ratio relative to the whole thickness, whereby the size of the flaw is measured. This method can be effectively adapted when the shape of flaw does not change, but is not effective for detecting flaws of a variety of shapes such as cracks in an object, since the phase does not change linearly in such cases.